FORK(2) FORK(2)
NAME
fork, rfork - manipulate process resources
SYNOPSIS
int fork(void)
int rfork(int flags)
DESCRIPTION
Forking is the only way new processes are created. The
flags argument to rfork selects which resources of the
invoking process (parent) are shared by the new process
(child) or initialized to their default values. The
resources include the file name space, the open file
descriptor table (which, when shared, permits processes to
open and close files for other processes), the set of envi-
ronment variables (see env(3)), the note group (the set of
processes that receive notes written to a member's notepg
file; see proc(3)), and open files. Flags is the logical OR
of some subset of 336168.if 432.sp 40u
RFPROC
If set a new process is created; otherwise changes
affect the current process. 360192.if 456.sp 40u
RFNAMEG
If set, the new process inherits a copy of the parent's
name space; otherwise the new process shares the
parent's name space. Is mutually exclusive with
RFCNAMEG.
RFNOWAIT
If set, the child process will be disassociated from
the parent. Upon exit the child will leave no Waitmsg
(see wait(2)) for the parent to collect.
RFCNAMEG
If set, the new process starts with a clean name space.
A new name space must be built from a mount of an open
file descriptor. Is mutually exclusive with RFNAMEG.
RFENVG
If set, the environment variables are copied; otherwise
the two processes share environment variables. Is
mutually exclusive with RFCENVG.
RFCENVG
If set, the new process starts with an empty environ-
ment. Is mutually exclusive with RFENVG.
RFNOTEG
Each process is a member of a group of processes that
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FORK(2) FORK(2)
all receive notes when a note is written to any of
their notepg files (see proc(3)). The group of a new
process is by default the same as its parent, but if
RFNOTEG is set (regardless of RFPROC), the process
becomes the first in a new group, isolated from previ-
ous processes.
RFFDG
If set, the invoker's file descriptor table (see
intro(2)) is copied; otherwise the two processes share
a single table.
RFCFDG
If set, the new process starts with a clean file
descriptor table. Is mutually exclusive with RFCFDG.
RFMEM
If set, the kernel will mark segments of type data and
bss as shared. The child will then inherit all the
shared segments the parent process owns. Other segment
types will be unaffected. Subsequent forks by the par-
ent will then propagate the shared data and bss between
children. The stack segment is always split. May be
set only with RFPROC.
File descriptors in a shared file descriptor table are kept
open until either they are explicitly closed or all pro-
cesses sharing the table exit.
If RFPROC is set, the value returned in the parent process
is the process id of the child process; the value returned
in the child is zero. Without RFPROC, the return value is
zero. Process ids range from 1 to the maximum integer (int)
value. Rfork will sleep, if necessary, until required pro-
cess resources are available.
Fork is just a call of rfork(RFFDG|RFPROC).
SEE ALSO
intro(2), proc(3),
DIAGNOSTICS
These functions set errstr.
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